Roman Numeral Converter
Convert numbers to Roman numerals and Roman numerals back to numbers, with validation.
Formula last reviewed 15 September 2026 · How we verify our calculators
Roman numeral
MCMXCIV
Updates live as you type
Frequently asked questions
Letters represent values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. They are added left to right, except when a smaller value precedes a larger one (IV=4, IX=9), where it is subtracted.
Standard Roman numerals go up to 3999 (MMMCMXCIX). Larger numbers need overline notation, which this converter does not use.
Those are non-standard. The converter validates by re-encoding the value, so it flags malformed numerals instead of silently returning a wrong number.
Clock faces, book chapters, movie sequels, monarch and pope names, and the year in film credits and monuments.
MCMXCIV, and the rule that makes it tricky
The number 1994 converts to MCMXCIV — and reading it back requires understanding one rule that most explanations skip.
Breaking it down: M (1000) + CM (900) + XC (90) + IV (4) = 1994.
Note that CM is not C + M. It is 900, expressed by placing a smaller numeral before a larger one to mean subtraction.
The symbols
- I = 1
- V = 5
- X = 10
- L = 50
- C = 100
- D = 500
- M = 1000
The additive and subtractive rules
Additive — where a numeral is followed by one of equal or lesser value, add them. VI = 5 + 1 = 6. MMX = 1000 + 1000 + 10 = 2010.
Subtractive — where a smaller numeral precedes a larger one, subtract. IV = 5 − 1 = 4. IX = 9. XL = 40. XC = 90. CD = 400. CM = 900.
The subtractive rule is constrained, and this is where most hand-written Roman numerals go wrong. Only six subtractive pairs are valid:
IV (4), IX (9), XL (40), XC (90), CD (400), CM (900)
The pattern: only I, X and C may be subtracted, and only from the next two larger symbols. So IL for 49 is invalid — 49 is XLIX (40 + 9). IC for 99 is invalid — 99 is XCIX. And VX, LC and DM are never valid, because V, L and D are never subtracted.
Other rules
No symbol repeats more than three times consecutively. 4 is IV, not IIII. 40 is XL, not XXXX. (Clock faces are the famous exception, traditionally using IIII for 4 for reasons of visual balance.)
V, L and D never repeat at all, since VV would simply be X.
The largest possible standard numeral is 3,999 — MMMCMXCIX. Beyond that, the classical system used a vinculum, an overbar multiplying the value by 1,000, which is difficult to represent in plain text.
There is no zero. The Roman system has no symbol for nothing and no concept of positional place value, which is precisely why it is unsuited to arithmetic and why the Hindu-Arabic system replaced it.
Where they are still used
Copyright and film credit dates, traditionally.
Book chapters, prefaces and volume numbers, and outline numbering in formal documents.
Monarchs and popes — Elizabeth II, Charles III.
Clock and watch faces.
Sporting events — Super Bowl and Olympiad numbering.
Building cornerstones and monuments, where the form carries a deliberate weight.
Converting by hand
To Roman: work from the largest value down, subtracting as you go. For 1994 — subtract 1000 (M, leaving 994), then 900 (CM, leaving 94), then 90 (XC, leaving 4), then 4 (IV). Result: MCMXCIV.
To number: read left to right; if a numeral is smaller than the one after it, subtract it, otherwise add it.
Common mistakes
Inventing subtractive pairs. Only the six listed are valid; IL, IC and VX are not.
Writing IIII instead of IV. Valid on clock faces by convention, incorrect otherwise.
Repeating V, L or D. They never repeat.
Exceeding 3,999 without a vinculum. The standard system stops there.
Expecting a zero. The system has none.